Patent Document 1: Japanese Patent Application Laid open No. 2000-258254 “Temperature Recording Device”
There is a sensor tag device as a device, which is disposed to an article or a container to measure information of a time that varies every second at regular time intervals and from which a temperature history can be read at a later stage by utilizing a wireless communication line.
This sensor tag device can be disposed to many kinds of objects or places extensively and information can be readily read therefrom. Therefore, it can be considered that this device becomes an element technology, which realizes a radically new infrastructure in a future network society, which is called a sensor fusion if network connection can be achieved.
At the present time, an active type sensor tag device having a battery or a passive type sensor tag which is utilized at a short range of approximately several-ten cm without having a history function has been mainly studied and developed.
Thus, it is considered that an application range can be further widened if a passive type sensor tag device which has a history function without a battery and from which information can be read at a position distanced by 10 m or more can be realized. It is to be noted that an inquirer is used for such a reading operation.
For example, there is a situation where confirming a history of a change in an ambient temperature or a history of, e.g., light/vibrations at a later stage is desirable in regard to foods or some of industrial products, or a situation where confirming a history of, e.g., a load (strain or acceleration) on buildings or large constructions after an earthquake and others at a later stage is desirable. It is to be noted that various kinds of conditions, e.g., a monitoring target/history target, which varies depending on each industry segment, will be referred to as events hereinafter.
Extensively arranging many kinds of sensor tag devices, which do not require maintenance, e.g., replacing a battery in this manner enables constructing a new information system or safety management system that
FIG. 5 is a block diagram of a sensor tag device showing a conventional sensor tag device disclosed in Patent Document 1.
A thermistor 503 is connected with an internal bridge, and its output temperature signal is converted into digital information by an AD converter 511. This operation is intermittently performed, and its output information is stored in a non-volatile memory 512 A temperature recording interval is set by an external command. These operations are controlled by a microcomputer 515 and necessary arithmetic operations are executed. Further, its operation power is supplied through a supply path 517 designated as a power supply (1) from a power supply circuit 514. During this period, necessary clocks are constantly supplied from an oscillation circuit 516.
In the sensor tag device, although an internal measurement recording circuit operates with a power supplied from a battery 504 in a short period where a temperature is measured and recorded, minimum circuits, e.g., a clock circuit and a monitoring circuit alone operate in an idle period between such periods to suppress wastage of the battery.
When controlling this device from the outside and reading Information, a high-frequency current modulated based on a digital signal is flowed to a coil 501 from an external reader/writer. A coil 502 senses this current to demodulate digital information and supplies it to a microcomputer 515. At the same time, a high-frequency electromotive force induced in the coil 502 is rectified and smoothed to turn to a power, and it is supplied to a memory 512 and the microcomputer 515 through a supply path 518 designated as a power supply (2). The above-explained operation enables issuing a command, e g., initial setting or starting reading to the device side. It is to be noted that an arrow 519 of a dotted line or the like in FIG. 5 denotes a flow of information.
When returning information to the outside from the device side, the information is read from the memory based on a command from the microcomputer 515, modulated to a high frequency by a rectification/demodulation/modulation circuit 513, and supplied to the outside. This modulation mode is a mode of modulating a high frequency supplied from the outside through the coil 501, thereby avoiding wastage of the battery 504 without requiring an internal power
It is to be rioted that modulating and using a high frequency oscillated inside in place of modulating a high frequency supplied from the outside through the coil 501 enables assuring a large distance from the reader/writer (inquirer). However, in this case, since an oscillation power is supplied from the battery 504, a consumption amount of the battery is increased